1. Field of the Invention
The present invention relates to a solid-state image sensor and camera.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2001-250931 discloses a solid-state image sensor having a focus detection function. Such a solid-state image sensor forms two images having a disparity by dividing a photodiode in each pixel for focus detection into two. By detecting a phase difference between these two images, a defocus amount can be obtained.
When the solid-state image sensor having the focus detection function is applied to a camera with an interchangeable lens, imaging lenses having various numerical apertures (NA), that is, f-numbers, are likely to be used. In order to put into a practical use as a camera system, it is required to satisfy characteristics of a given criterion or higher for every interchangeable lens.
A microlens provided to the solid-state image sensor is designed so that its focal point position matches near the surface of a photodiode. Incoming light through an imaging lens with a large f-number forms a small light spot on a photodiode. On the other hand, incoming light through a lens with a small f-number forms a large light spot on a photodiode. Therefore, in order to obtain constant luminous sensitivity in imaging lenses having various f-numbers, a microlens should be designed so that a light spot can be prevented from protruding from a photodiode portion as much as possible even when an imaging lens with a small f-number is used.
On the other hand, two divided photodiodes, which are arranged in each pixel to obtain phase-difference signals for focus detection, are arranged to be close to each other. A charge generated by light, which enters near a boundary between the two photodiodes, is likely to be accumulated by both the two photodiodes. A phenomenon where a charge generated by light entering one photodiode is accumulated by the other photodiode can be considered as crosstalk, which may lower the phase-difference detection precision and speed.